Otosclerosis: Causes, Symptoms, and Treatment
Otosclerosis is the result of abnormal bone growth of the cancellous bone found in the middle ear. It causes progressive hearing loss, especially in young adults.
This abnormal bone growth leads to the failure of the ossicles in the middle ear to vibrate, a vital mechanism for sound production. From the point of view of the origin of the terms, it comes from the words oto, which means ‘ear’, and sclerosis, which refers to ‘hardening’.
The exact cause is unknown and there’s no specific pharmacological treatment. The approach is to regulate the effects of the hearing loss.
Otosclerosis is caused by abnormal bone remodeling
Abnormal bone remodeling is a pathological process. There’s a removal of mature bone, due to destruction by osteoclasts that are responsible for replacing this tissue with new tissue. The new bone tissue in otosclerosis is very thick, with many cells, and is quite vascularized.
This is why the process is called stapedostomy. It mainly affects the oval window and predominantly involves the stapes.
When the stapes are involved, the abnormal bone growth fixes it in a position that prevents vibration and the transmission of the sound wave. In this way, conduction hyperacusis (reduced hearing ability) is produced, because the conduction of sound waves is affected.
The mechanism by which hearing is affected is due to the fact that the vibration of the ossicles (hammer, anvil, and stirrup) of the middle ear is impeded. Without this movement, there’s no transmission of sound waves.
The sound waves cause the eardrum to vibrate, and these waves then travel to the three ossicles in the middle ear to amplify the impulse. They’re then sent to the cochlea.
The cochlea is located in the inner ear and is responsible for creating an electrical signal with the movement of chemicals. Finally, the auditory nerve transmits the information to the cerebral cortex.
The cause of otosclerosis is not fully understood
Although the exact cause is unknown, it’s attributed to hereditary factors in most cases. It’s considered an autosomal dominant disease with incomplete penetrance (there’s a 20-25% risk in offspring if a parent has it).
It’s more common in females, between the second and fifth decade of life, and in Caucasians. In addition, up to 80% of the time it’s bilateral. In the case of being unilateral, it predominantly affects the right ear.
The predominance of the female sex is associated with endocrinological factors. Estrogen levels in women of reproductive age may promote osteoclast activity, initiating bone remodeling.
In addition to heredity, otosclerosis is associated with chronic varicella or measles virus infection, low serum sodium fluoride levels, and immune system disorders. It may also be caused by stress fractures of the bone tissue surrounding the inner ear.
The main symptom is hearing loss of insidious onset, with slow and progressive progression. The average progression of otosclerosis to total hearing loss is 7 years. In some cases tinnitus (ringing in both ears), vertigo, dizziness, and balance problems are associated.
Otosclerosis should be suspected in any young adult with progressive hearing loss.
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The diagnosis is clinical
The initial suspicion is clinical and is complemented with audiological studies that demonstrate conductive hearing loss. Compatible clinical findings plus an audiometry with conductive hearing loss are sufficient for a specific diagnosis.
Imaging studies are reserved only for confirmation of doubtful cases. High-resolution computed tomography of the temporal bone is the method of choice in these cases. Magnetic resonance imaging may also be recommended.
At the time of evaluation, during the physical examination with otoscopy, reddened areas in the middle ear are visible through the healthy tympanic membrane.
Regarding audiometry, there’s a decrease in the bone conduction threshold, due to stapes fixation. CT scans show areas of reduced density in defined areas of the temporal bone.
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Treatment and prognosis of otosclerosis
There’s no specific pharmacological treatment. Otosclerosis progresses slowly and progressively, and, when diagnosed early, it isn’t always necessary to attempt surgery.
In mild cases, it can be treated with ear implants that amplify the sound. In other cases, vitamin D, calcium, or fluoride are indicated.
When surgery is required, a procedure called stapedectomy is performed. In this intervention, part, or all, of the stapes piece are removed and replaced by a prosthesis that allows the conduction of sound waves.
Treatment involves developing skills to combat hearing loss (such as learning sign language).
The treatment of otosclerosis is focused on improving hearing and requires strict follow-up with an otolaryngologist, with periodic audiometries to control the growth of the bone and avoid total hyperacusis.It might interest you...